Ryan Anderson is a graduate student at Cornell University. He has a background in astronomy and physics, but now spends his days studying Mars. His research focuses on preparing for the upcoming Mars Science Laboratory mission by studying potential landing sites and shooting rocks with lasers.
We’ve all seen pictures of erupting terrestrial volcanoes from space, and even eruptions on Jupiter’s moon Io in the outer solar system, but would it be possible to detect an erupting volcano on an exoplanet? Astronomers say the answer is yes! (with a few caveats)
It’s going to be decades before telescopes will be able to resolve even the crudest surface features of rocky extrasolar planets, so don’t hold your breath for stunning photos of alien volcanoes outside our solar system. But astronomers have already been able to use spectroscopy to detect the composition of exoplanet atmospheres, and a group of theorists at the Harvard-Smithsonian Center for Astrophysics think a similar technique could detect the atmospheric signature of exo-eruptions.
By collecting spectra right before and right after the planet goes behind its star, astronomers can subtract out the star’s spectrum and isolate the signal from the planet’s atmosphere. Once this is done, they can look for evidence of molecules common in volcanic eruptions. Models suggest that sulfur dioxide is the best candidate for detection because volcanoes produce it in huge quantities and it lasts in a planet’s atmosphere for a long time.
Still, it won’t be easy.
“You would need something truly earthshaking, an eruption that dumped a lot of gases into the atmosphere,” said Smithsonian astronomer Lisa Kaltenegger. “Using the James Webb Space Telescope, we could spot an eruption 10 to 100 times the size of Pinatubo for the closest stars,” she added.
In 1991 Mount Pinatubo in the Philippines belched 17 million tons of sulfur dioxide into the stratosphere. Volcanic eruptions are ranked using the Volcanic Explosivity Index (VEI). Pinatubo ranked ‘colossal’ (VEI of 6) and the largest eruption in recorded history was the ‘super-colossal’ Tambora event in 1815. With a VEI of 7 it was about 10 times as large as Pinatubo. Even larger eruptions (more than 100 times larger than Pinatubo) on Earth are not unheard of: geologic evidence suggests that there have been 47 such eruptions in the past 36 million years, including the eruption of the Yellowstone caldera about 600,000 years ago.
The best candidates for detecting extrasolar volcanoes are super-earths orbiting nearby, dim stars, but the Kaltenegger and her colleagues found that volcanic gases on any earth-like planet up to 30 light years away might be detectable. Now they just have to wait until the James Webb Space Telescope is launched 2014 to test their prediction.
There’s something strange going on around the red giant star CW Leonis (a.k.a. IRC+10216). Deep within the star’s carbon-rich veil, astronomers have detected water vapor where no water should be.
CW Leonis is similar in mass to the sun, but much older and much larger. It is the nearest red giant to the sun, and in its death throes it has hidden itself in a sooty, expanding cloud of carbon-rich dust. This shroud makes CW Leonis almost invisible to the naked eye, but at some infrared wavelengths it is the brightest object in the sky.
Water was originally discovered around CW Leonis in 2001 when the Submillimeter Wave Astronomy Satellite (SWAS) found the signature of water in the chilly outer reaches of the star’s dusty envelope at a temperature of only 61 K. This water was assumed to be evidence for vaporizing comets and other icy objects around the expanding star. New observations with the SPIRE and PACS spectrometers on the Herschel Space Observatory reveal that there’s something much more surprising going on.
“Thanks to Herschel’s superb sensitivity and spectral resolution, we were able to identify more than 60 lines of water, corresponding to a whole series of energetic levels of the molecule,” explains Leen Decin from the University of Leuven and leader of the study. The newly-detected spectral lines indicate that the water vapor is not all in the cold outer envelope of the star. Some of it is much closer to the star, where temperatures reach 1000 K.
No icy fragments could exist that close to the star, so Decin and colleagues had to come up with a new explanation for the presence of the hot water vapor. Hydrogen is abundant in the envelope of gas and dust surrounding carbon stars like CW Leonis, but the other building block of water, oxygen, is typically bound up in molecules like carbon monoxide (CO) and silicon monoxide (SiO). Ultraviolet light can split these molecules, releasing their stored oxygen, but red giant stars don’t make much UV light so it has to come from somewhere else.
The dusty envelopes around carbon stars are known to be clumpy, and that turns out to be the key to explaining the mysterious water vapor. The patchy structure of the shroud around CW Leonis lets UV light from interstellar space into the depths of the star’s envelope. “Well within the envelope, UV photons trigger a set of reactions that can produce the observed distribution of water, as well as other, very interesting molecules, such as ammonia (NH3),” says Decin. “This is the only mechanism that explains the full range of the water’s temperature.”
In the coming months, astronomers will test this hypothesis by using Herschel to search for evidence of water near other carbon stars.
White sand, blue water, sunny skies, pina coladas. When you think of “extreme environments” I doubt the Caribbean is high on your list. But a team of scientists from Woods Hole Oceanographic institute and NASA’s Jet Propulsion Laboratory, exploring the 68-mile-long Mid-Cayman rise deep beneath the surface of the Caribbean, have discovered the deepest known hydrothermal vent in the world, along with two other distinct types of vents.
The mid-Cayman rise is a much smaller version of the mid-ocean ridge system, a chain of submarine mountains that encircles the globe. These ridges form in locations where tectonic plates are pulling apart, allowing mantle rocks to melt and emerge at the surface as lava. Seawater, percolating through the hot rocks at these spreading centers, is superheated and emerges at vents, bearing a rich bounty of dissolved nutrients to support thriving ecosystems that can live without any sunlight.
“This was probably the highest-risk expedition I have ever undertaken,” said chief scientist Chris German, a Woods Hole Oceanographic Institution geochemist who has pioneered the use of autonomous underwater vehicles to search for hydrothermal vent sites. “We know hydrothermal vents appear along ridges approximately every 100 kilometers [62 miles]. But this ridge crest is only 100 kilometers long, so we should only have expected to find evidence for one site at most. So finding evidence for three sites was quite unexpected – but then finding out that our data indicated that each site represents a different style of venting – one of every kind known, all in pretty much the same place – was extraordinarily cool.”
In addition to the deepest hydrothermal vent yet discovered, at a depth of 5,000 meters (16,400 feet), the team also found a shallower low-temperature vent. Only one other vent of this type has been discovered: the famous “Lost City” vent in the Atlantic.
“We were particularly excited to find compelling evidence for high-temperature venting at almost 5,000 meters depth,” said Julie Huber, a scientist in the Josephine Bay Paul Center at the Marine Biological Laboratory in Woods Hole. “We have absolutely zero microbial data from high-temperature vents at this depth.”
The ecosystems encrusting the deep sea vents on the mid-Cayman rise provide valuable clues to how life could arise and thrive elsewhere in the solar system. “Most life on Earth is sustained by food chains that begin with sunlight as their energy source. That’s not an option for possible life deep in the ocean of Jupiter’s icy moon Europa,” said JPL co-author Max Coleman.
With an airless sky, intense radiation, icy crust, and no pina coladas, the surface of Europa is about as different from the Caribbean as you can get. But deep on the sea floor, they may be remarkably similar.
“Organisms around the deep vents get energy from the chemicals in hydrothermal fluid, a scenario we think is similar to the seafloor of Europa,” Coleman said. “This work will help us understand what we might find when we search for life there.”
An artist's depiction of a future Europa mission. Image credit: NASA
If you take a lot of digital pictures, you’re probably familiar with the frustration of keeping track of dozens of files, and always running out of hard drive space to store them. Well, the scientists and engineers on NASA’s Wide-field Infrared Survey Explorer (WISE) mission have no pity for you. Their spacecraft just finished photographing the entire sky in exquisite detail: a total of 1.3 million photos.
“The eyes of WISE have not blinked since launch,” said William Irace, the mission’s project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Both our telescope and spacecraft have performed flawlessly and have imaged every corner of our universe, just as we planned.”
WISE surveys the sky in strips as it orbits the earth. It takes six months of constant observing to map the entire sky. By pointing at every part of the sky, astronomical surveys deliver excellent data covering both well-known objects and those that have never been seen before.
“WISE is filling in the blanks on the infrared properties of everything in the universe from nearby asteroids to distant quasars,” said Peter Eisenhardt of JPL, project scientist for WISE. “But the most exciting discoveries may well be objects we haven’t yet imagined exist.”
One example of a well-known object seen in new light by WISE is the Pleiades cluster: a group of young blue stars shrouded by dust that the cluster is currently passing through. In WISE’s false-color infrared vision, the hot stars look blue but the cooler dust clouds give off longer wavelengths of infrared light, causing them to glow in shades of yellow and green.
The WISE survey is particularly significant because such a wide range of objects in the universe are visible in infrared light. Giant molecular clouds glow in infrared light, as do brown dwarfs – objects that are bigger than planets but smaller than true stars. WISE can also see ultra-bright, extremely distant galaxies whose visible light has been stretched into the infrared by the expansion of the universe during its multi-billion-year journey.
The recently completed WISE survey also observed 100,000 asteroids in our solar system, many of which had never been seen before. 90 of the newly discovered asteroids are near-earth objects, whose orbits cross our own, making them potentially dangerous but also potential targets for future mission.
You might think that 1.3 million pictures would be plenty, but WISE will keep mapping the sky for another three months, covering half of the sky again and allowing astronomers to search for changes. The mission will end when the spacecraft’s solid hydrogen coolant finally runs out and the infrared detectors warm up (they don’t work as well when they are warm enough to emit the same wavelengths of infrared light that they are meant to detect).
But even as the telescope warms up, the astronomers on the WISE team will just be getting warmed up too. With nearly two million images, they will be busy making new discoveries for years to come.
Next time you hear someone complaining that it’s too hot outside, you can make them feel better by pointing out that at least their planet isn’t so hot it is vaporizing into space. Unless of course you happen to be speaking to someone from the gaseous extrasolar planet HD 209458b.
New observations from the Hubble Cosmic Origins Spectrograph (COS) confirm suspicions from 2003 that the planet HD 209458b is behaving like a Jupiter-sized comet, losing its atmosphere in a huge plume due to the powerful solar wind of its too-close star.
HD 209458b is a “hot Jupiter”: a gas giant that orbits extremely close to its star. It whips around its star in 3.5 days, making even speedy little Mercury with its 88 day orbit around the sun look like a slacker.
Astronomers have managed to learn a lot about HD 209458b because it is a transiting planet. That means that its orbit is aligned just right, so from our point of view it blocks some of the light from its star. When that happens, it gives hints at the planet’s size, and gives a much better constraint on the mass. HD 209458b is a little more than two thirds the mass of Jupiter, but heat from its star has puffed it up to two and a half times Jupiter’s diameter.
In the case of HD 209458b, during transits some of the star’s light passes through the planet’s escaping, 2,000-degree-Fahrenheit atmosphere, allowing scientists to tell what it is made of and how fast it is being lost to space.
“We found gas escaping at high velocities, with a large amount of this gas flowing toward us at 22,000 miles per hour,” said astronomer Jeffrey Linsky of the University of Colorado in Boulder, leader of the COS study. “This large gas flow is likely gas swept up by the stellar wind to form the comet-like tail trailing the planet.”
The escaping planetary gases absorbed starlight at wavelengths characteristic of heavier elements like carbon and silicon, suggesting that the star’s intense heat is driving circulation deep in HD 209458b’s atmosphere, dredging up material that would otherwise remain far beneath lighter elements like hydrogen.
Even though its atmosphere is constantly streaming away into space, HD 209458b won’t be disappearing anytime soon. At the measured rate of loss, the planet would last about a trillion years, far longer than the lifetime of its host star.
So, be thankful that even on hot summer days, your planet is in no danger of being vaporized by its star. And if you do happen to be speaking to someone from HD 209458b, you can reassure them that their planet will still be there when they return home. Well, most of it, anyway.
New results published in the journal Icarus suggest that caves on Mars may provide future astronauts with more than just shelter. In many locations, even far from the poles, the caves may actually trap water ice.
Ice caves are made of rock, but they contain ice year-round. (Not to be confused with glacier caves, which are caves made of ice!) Ice caves can be found on the Earth even where surface temperatures are above freezing for months at a time. This happens because cold winter air sinks into the cave and is trapped, but during the summer, the circulation in the cave shuts off: it is full of dense cold air so the warm air outside can’t get in.
Now, in a study led by Kaj Williams of NASA Ames, scientists have used simulations of the global climate and assumptions about the thermal properties of the surface to figure out where on Mars similar cold-trapping might occur. Their results show that a significant portion of the martian surface has the right conditions for ice to accumulate in caves.
Even more tantalizing, the huge volcanic provinces of Tharsis and Elysium look to be particularly good at accumulating ice. This is important because caves formed by collapsing lava tubes have been seen on the flanks of these volcanoes. Lava tube caves on Earth tend to have limited air circulation, making them good candidates for ice accumulation.
Astronauts on the surface of Mars will likely need to take cover underground to avoid the harsh radiation environment of the surface. Natural caves such as lava tubes have been suggested as ideal ready-made shelters for astronauts, and they are only looking better. Not only could ice caves provide water as a resource, the ice could preserve valuable records of past climate cycles, and the caves may be important habitats for past or present martian life.
Williams and his team plan to continue refining their models, particularly focusing on the Tharsis and Elysium regions, using higher-resolution atmospheric models and more precise geologic data to pinpoint areas that are best for cave-ice formation.
The shape of the two-mile-tall Texas-sized ice cap at the north pole of Mars has puzzled scientists for forty years, but new results to be published in a pair of papers in the journal Nature on May 27 have put the controversy to rest.
The polar caps of Mars have been known since the first telescopic views of the planet, but early spacecraft images revealed that the north polar cap is scored by enigmatic troughs that spiral out from its center, as well as a chasm larger than the Grand Canyon. The origin of these features has been debated since they were first discovered in 1972.
One hypothesis to explain the giant canyon, called Chasma Boreale, is that volcanic heat melted the ice and caused a catastrophic flood that formed the chasm. Other scientists have suggested that wind sweeping downhill from the top of the cap carved Chasma Boreale from the ice.
Multiple explanations have been suggested for the spiral troughs too. One explains the troughs as fractures caused by the flow of ice from the pole. Another uses a model to suggest that the troughs are the natural result of solar heating and lateral heat conduction in the ice.
The two new papers, led by Jack Holt and Isaac Smith of The University of Texas at Austin’s Institute for Geophysics, used data from the Shallow Subsurface Radar (SHARAD) on the Mars Reconnaissance Orbiter (MRO) to study the internal structure of the ice cap and discover the origin of the troughs and the chasm.
“SHARAD sends pulses of radio waves from orbit, 700 times per second,” Holt explained. “Some energy is reflected from the surface, and then from subsurface interfaces if the intervening material allows the radio waves to penetrate. Radar at this wavelength (about 20 meters) penetrates ice very well, and it has been used from airplanes on Earth to map large portions of Earth’s ice sheets.”
“By putting all of the reflections together one can make an image of what lies beneath the
surface,” Smith added.
Holt explained that the ability to map not only the surface features but also the internal structure of the ice cap “opens the door to better understand what we see on the surface by providing critical context in time.”
By mapping the three-dimensional structure of the north polar ice cap, Smith and Holt have determined that both the troughs and Chasma Boreale were formed by katabatic winds, which blow down from the top of the ice cap.
“We aren’t saying they were carved by wind, rather that wind had a strong role in their formation and evolution.” Holt said. “Chasma Boreale is an old feature that persisted because new ice did not accumulate there, likely due to persistent winds coming from the highest point on the ice cap.”
Holt also discovered evidence for another old canyon that has been completely filled in over time. “No evidence remains on the surface to indicate that it was there previously,” Holt said. “We can map it in the radar data, however.”
The spiral troughs likewise are controlled by the wind. “The radar layers we see show evidence for wind transport because they vary in thickness and elevation [across the troughs],” Smith, lead author of the trough paper, explained. “The wind moves across the trough instead of through it [and] moves ice from the upwind side (thereby thinning they layer) to the downwind side (adding more to the existing layer).”
This causes the spiral troughs to migrate upwind over time, a phenomenon first proposed by Alan Howard, a researcher at the University of Virginia, in 1982. “Many people proposed other hypotheses suggesting he was wrong,” Smith said. “But when you look at a hypothetical cross section from his paper, it looks almost exactly like what we see in the radar data. We were amazed at how accurate Alan Howard predicted what we would
The troughs are spiral shaped due to the planet’s rotation. As the katabatic winds blow from the center of the cap down to lower latitudes they are twisted by the same “coriolis force” that causes hurricanes to spiral on the Earth.
The layers that Holt and Smith mapped using radar data also suggest that ice flows are much rarer on Mars than they are on Earth. The lack of flows means that the polar ice on Mars preserves more complex layers than expected. “This complexity provides very specific constraints on the climatic processes responsible for [the layers],” Holt said. “We will eventually be able to reconstruct winds and accumulation patterns across the polar cap and through time.”
Holt plans to use the ancient polar landscapes inferred from the SHARAD data along with simulations of the martian climate to model the formation of the polar cap. “If we can recreate the major features such as Chasma Boreale [in the models], then we will have learned a great deal about climate on Mars during that period.”
Smith and Holt also plan to study the effect of Mars’ tilt on the formation of the ice cap. “Because Mars’ orbit and tilt change so much with respect to the sun, it would be nice to see how that has affected deposition of ice on the cap. This requires much more mapping, and we have already begun that process,” Smith said.
“There is still much research to do on Mars,” Smith said. “The planet has a lot of mysteries, some of which we haven’t even found yet.”
An artist’s rendition of colliding planets, the most likely explanation for the warm dust observed around HD 131488. Image credit: Lynette Cook for Gemini Observatory/AURA
Five-hundred light years away, worlds are colliding, and they’re made of nothing we’ve ever seen.
Last week at the 215th American Astronomical Society meeting, UCLA astronomers announced that they had found warm dust – evidence for the violent collision of rocky planets – around a star called HD 131488. The strange thing is, the composition of the dust has little in common with the composition of rocky bodies in any other known system.
“Typically, dust debris around other stars, or our own Sun, is of the olivine, pyroxene, or silica variety, minerals commonly found on Earth,” said Dr. Carl Melis, who led the research as a graduate student at UCLA. “The material orbiting HD 131488 is not one of these dust types. We have yet to identify what species it is – it really appears to be a completely alien type of dust.”
The warm dust in the HD 131488 system is concentrated in an area close to the star, where temperatures are similar to those on Earth. The researchers concluded that the most likely source for dust in that part of the system would be the collision of two rocky planetary bodies. Only five other stars like HD 131488 with dust in their terrestrial planet zone are known. “Interestingly, all five of these stars have ages in the range of 10-30 million years,” Melis said. “This finding indicates that the epoch of final catastrophic mass accretion for terrestrial planets, the likes of which could have resulted in the formation of the Earth-Moon system in our own Solar System, occurs in this narrow age range for stars somewhat more massive than the Sun.”
The team also discovered a unique second dusty region in the outer reaches of the HD 131488 system, comparable to the location of Pluto and other Kuiper Belt objects in our own solar system.
Top: Illustration depicting the location of the warm and cold dust rings in the HD131488 system. Bottom: Comparable regions in our own solar system, with the orbits of the outer planets for scale. Image Credit: Lynette Cook for Gemini Observatory/AURA
“The hot dust almost certainly came from a recent catastrophic collision between two large rocky bodies in HD 131488’s inner planetary system,” Melis said. “The cooler dust, however, is unlikely to have been produced in a catastrophic collision and is probably left over from planet formation that took place farther away from HD 131488.”
“…for some reason stars that have large amounts of orbiting warm dust do not also show evidence for the presence of cold dust. HD 131488 dramatically breaks this pattern,” said Dr. Benjamin Zuckerman, a co-author on the paper and a professor of physics and astronomy at UCLA.
With its unusual dust composition and unique combination of warm and cold dust regions, the HD 131488 system is now under intense scrutiny. Melis and colleagues plan to continue trying to determine the composition of the dust, and will search for other stars with the dusty evidence for planet formation.
This illustration shows the visible Milky Way galaxy surrounded by a “squashed beachball”-shaped dark matter halo. Source: UCLA
Our galaxy is shaped like a flat spiral right? Not if you’re talking about dark matter. Astronomers announced today that the Milky Way’s dark matter halo, which represents about 70% of the galaxy’s mass, is actually shaped like a squashed beachball.
Dark matter is completely invisible, but it still obeys the law of gravity, so the existence of dark matter haloes, and their shape, can be inferred by monitoring the orbits of dwarf galaxies orbiting the much larger Milky Way.
Unfortunately, to determine the orbit of an object, you have to measure its position at several points in that orbit, and dwarf galaxies take about a billion years to go around the Milky Way. Astronomers just haven’t been around long enough to watch even a fraction of a complete orbit. Luckily, they don’t have to.
Dwarf galaxies, just like their full-sized counterparts, and made of billions of stars. When the tidal forces from a big galaxy like the Milky Way act on a dwarf galaxy, the result is a streamer of stars that trace out the dwarf galaxy’s orbit. By using data from huge all-sky surveys, a group of astronomers led by David Law at UCLA were able to reconstruct the orbit of the Sagittarius Dwarf Galaxy. There was just one problem: different parts of the dwarf galaxy had different orbits, which led to wildly different dark matter halo shapes.
Law and his colleagues Steven Majewski (University of Virginia) and Kathryn Johnston (Columbia University) solved this problem by allowing models of the dark matter halo to be “triaxial” – in other words, have different lengths in all three dimensions. The best model solution results in a halo shaped like a beach ball that has been squashed sideways.
“We expected some amount of flattening based on the predictions of the best dark-matter theories,” said Law, “but the extent, and particularly the orientation, of the flattening was quite unexpected. We’re pretty excited about this, because it begs the question of how our galaxy formed in its present orientation.”
Sagittarius is not the only dwarf galaxy orbiting the Milky Way, and Law and his colleagues plan to study the orbits of other dwarf galaxies to refine their model. “It will be important to see if these results hold up as precise orbits are measured for more of these galaxies. In the meantime, such a squashed dark-matter halo is one of the best explanations for the observed data.”
This illustration shows the visible Milky Way galaxy (blue spiral) and the streams of stars represent the tidally shredded Sagittarius dwarf galaxy. Source: UCLA
This illustration shows a pulsar’s magnetic field (blue) creates narrow beams of radiation (magenta). Image credit: NASA
How do you detect a ripple in space-time itself? Well, you need hundreds of precision clocks distributed throughout the galaxy, and the Fermi gamma ray telescope has given astronomers a new way to find them.
The “clocks” in question are actually millisecond pulsars – city-sized, sun-massed stars of ultradense matter that spin hundreds of times per second. Due to their powerful magnetic fields, pulsars emit most of their radiation in tightly focused beams, much like a lighthouse. Each spin of the pulsar corresponds to a “pulse” of radiation detectable from Earth. The rate at which millisecond pulsars pulse is extremely stable, so they serve as some of the most reliable clocks in the universe.
Astronomers watch for the slightest variations in the timing of millisecond pulsars which might suggest that space-time near the pulsar is being distorted by the passage of a gravitational wave. The problem is, to make a reliable measurement requires hundreds of pulsars, and until recently they have been extremely difficult to find.
“We’ve probably found far less than one percent of the millisecond pulsars in the Milky Way Galaxy,” said Scott Ransom of the National Radio Astronomy Observatory (NRAO).
Data from the Fermi gamma-ray space telescope, which started collecting data in 2008, have changed the way millisecond pulsars are detected. The Fermi telescope has identified hundreds of gamma-ray sources in the Milky Way. Gamma rays are high-energy photons, and they are produced near exotic objects, including millisecond pulsars.
“The data from Fermi were like a buried-treasure map,” Ransom said. “Using our radio telescopes to study the objects located by Fermi, we found 17 millisecond pulsars in three months. Large-scale searches had taken 10-15 years to find that many.”
Ransom and collaborator Mallory Roberts of Eureka Scientific used the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT) to find eight of the 17 new pulsars.
Right now astronomers have only barely enough millisecond pulsars to make a convincing gravitational wave detection, but with Fermi to help identify more pulsars, the odds of detecting these ripples in space-time are steadily increasing.
Ransom and Roberts announced their discoveries today at the American Astronomical Society’s meeting in Washington, DC.